HI,
For a project we are working on it is useful to have the type resolvers have access to the context. As an example think of our data being a numerical ID that represents a person (interface type). That person can be an employee type or a customer type, and that needs to have access to the context to resolve which it is.

I've added a PR for this at #795

It would be really helpful if you could take a look. Many thanks for a great library!